Split interfaces_info between core and modules

GYP split step 3/4

Last remaining step (shown in FIXMEs) is the global constructors.

Needed to modify the interfaces_info merging function due to
existing of partial interface definitions that cross
components, primarily lots of
partial interface Navigator
in modules.
This is not a layering violation (since partial
interfaces *extend* interfaces), but it causes added
complexity.

One nice side effect:
touching a core IDL file means we now only need to parse all
core files, but not modules files, and conversely for
modules, which makes incremental build a bit faster.

R=haraken
TBR=thakis
BUG=358074

Review URL: https://codereview.chromium.org/304643003

git-svn-id: svn://svn.chromium.org/blink/trunk@174942 bbb929c8-8fbe-4397-9dbb-9b2b20218538